Datasheet

DS2786 Stand-Alone OCV-Based Fuel Gauge
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OCV CELL MODEL
The OCV cell model is a 9-point piece-wise linear approximation of open circuit cell voltage versus the remaining
capacity of the cell. Whenever an OCV update occurs, the Relative Capacity Register is adjusted to a new value
based on the OCV voltage reading and a linear approximation of the table values. Figure 15 shows the factory-
default cell model stored in EEPROM.
Figure 15. Default OCV Cell Model
3
3.2
3.4
3.6
3.8
4
4.2
0%20%40%60%80%100%
The OCV cell model can be modified by changing the Capacity and Voltage Breakpoint Registers in EEPROM.
Capacity 0 is fixed at 0% and cannot be changed. Capacity 1 through Capacity 7 are stored with 0.5% resolution at
addresses 61h through 67h respectively. Capacity values must be monotonic (Capacity 1 > Capacity 0, Capacity 2
> Capacity 1, etc.), but otherwise can be written to any value between 0.5% to 99.5%. Capacity 8 is fixed at a value
of 100% and cannot be changed.
Voltage breakpoints require two bytes per breakpoint, but are otherwise stored in a similar manner. Voltage
Breakpoint 0: MSB stored at address 68h, LSB stored at address 69h. Other voltage breakpoints stored
sequentially through address location 79h. Each voltage breakpoint has a resolution of 1.22mV, and a range from
0.0V to 4.996V (IC operation limited to 4.5V). Voltage breakpoint values must also be monotonic.
Figure 16. Capacity 1 to Capacity 7 Registers Format
Address 61h–67h
2
7
2
6
2
5
2
4
2
3
2
2
2
1
2
0
MSb LSb
Units: 0.5%
Breakpoint 8
4.171V
100%
Breakpoint 6
4.042
85%
Breakpoint 5
4.005
80%
Breakpoint 7
4.087V
90.5%
Breakpoint 4
3.831V
52.5%
Breakpoint 3
3.752
25%
Breakpoint 2
3.673V
10%
Breakpoint 1
3.619V
5%
Breakpoint 0
3.186V
0%